How much cow shit should go in one pot with one plant ?

Well let me tell you, If it's fresh manure, you don't even want to use it because it will burn your plants. I live on a cattle farm, and if it's somewhat aged, and you add some lime to it, a little soil, a hand ful of woodashes and a small very small amount of bone meal, the sky is the limit. Truely.

I have heard of bud being grown in aged cow manure and sand, 50/50.
Not suggesting this by any means, but once the stuff has cooked down a bit it can be very useful, especialy when mixed with other stuff. Robby makes a good call. If you want the sky to be the limit though It's got to compost at least a year IMO.
Are you getting by the load (trucked in) or by the bag?

right on robbie & organick...but if you want to see just how far down alice's rabbit hole you can go with the magic of cow shit, I strongly suggest you read about bio-dynamics. it may seem like 'snake oil' science, but seeing is believing. and b-d grown weed is unmatched in taste...period!